This much is known for a fact. Peter Philen Sr. appeared in South Carolina and is recorded as having applied for a South Carolina Militia pension in 1783. Therefore we can assume that he served in the Revolutionary War, serving in the state militia, around 1775 - 1780. He must have arrived some time previous to this, and we know that he settled in the Darlington District of Northwestern South Carolina.
Various spellings of the Philen name are found such as Filand, Fyland, Philan, and Phyland. The book, The Surnames of Ireland, by MacLysaght, gives the following: "Philan, see Phylan; Phylan, Fyland: these are usually variants of Phelan in use in Westmeath and north Offaly. Phylan, Philan and Fyland are extant in Offaly and adjacent areas where they are definitely for O'Faolain. Phylan may also be a distinct name, viz. O'Fialain a bardic family of Ulster, now rare and called Phelan." Westmeath and Offaly are counties in southern Ireland.
To further complicate matters, the correct spelling of the name, Philen, has been found in German (Rhineland) christening and marriage records in the late 1500s and mid 1600s. There is a section of Germany called Westphalia, that includes the Rhinelarid, near the border with the Netherlands. It is possible to speculate that a person from the area of Westphalia might be called a Phalian. Also, enlistment records from the Pennsylvania Militia show a Filing who lists his origin as Germany. Thus, there is a strong possibility that the name could be German in origin, dating from the early 1600s.
Now let's examine the migration and names of Peter Philen Sr. Peter married Fereby (Phereby) and their children were: Peter Jr., Mannasah, Riley, William, John, Fereby, Mary, Elizabeth, Sarah, and Jane. These are mostly biblical names. Thus, we can infer that Peter and Fereby had a great deal of religious influence in naming their children. Since one of the boys was named William, this can rule out Catholic as the religion, since no Catholic would name a child William, because of the suffering and persecution the Catholics suffered under William and Mary. By inference, this probably rules out migration from southern Ireland.
Peter Sr. moved to Alabama in 1819, settling in Lower Peachtree. The families that moved along with him were the Walkers, Kirks, Clarkes, Smiths, and Davis. The fact that these are Irish, Scottish, and Welsh names complicates the matter even more. I have documentation in the form of diaries and written histories that the Walkers and Clarkes moved from County Antrim, in northern Ireland, to America. The Kirks moved from Scotland to County Antrim, Ireland, and then to America. These people, having moved from northern Ireland, moved as a group, and at about the same time as Peter Sr., to the Wilcox and Clarke county areas of Alabama. The fact that the Walkers and Philens intermarried, suggests that this was a very closely knit community, and that everyone knew each other well. Also, northern Ireland was predominately Protestant whereas Southern Ireland was predominately Catholic. With Peter Sr's children having Protestant names, one could speculate that he might be from Northern Ireland.
Did Peter Sr. come from Northern Ireland? We don't have the definitive document stating where Peter said he came from. Perhaps it can be found in the S.C. Militia records. What about the correct spelling found in Germany in the 1600s? The name Philen is very difficult to find in Germany today, but during this time of the 1600s, there was frequent trade and movement between Scotland, Ireland, Holland, and Germany. Did the Philens originate in Western Germany (Westphalia) and move to County Antrim in the 1700s? That is a good possibility too. There was massive settlement of Northern Ireland by Scots and some Dutch by the English in an attempt to colonize Ireland with Protestants. Remember that Germany was Protestant too, because of the efforts of Martin Luther to overturn the Catholics there. It does seem unlikely that Peter Sr. moved to America directly from Germany since he settled with so many people that we know came from Ireland. Ethnic groups tended to settle together in this time because they needed to preserve some of their culture and heritage, for instance, Zimmerman is the only truly German name found in early Wilcox County.
The exact origin may never be definitively found, and much of what I have laid out here is speculation based on inference on my part, using the facts as I know them. An interesting side note: My wife and I were sitting in an outdoor restaurant several years ago in northern France. (Northeastern France, Eastern Belgium, Western Germany, and Eastern Holland all comprise the same geographical region.) She noted that in looking around the town square at the people, that I looked like all the locals, and that if I just kept my mouth shut, that I would fit right in.