I just wanted to say that Phelim is quite an interesting name.
Typically, I've found the more Irish names to be pretty rare or unfound in the 1800s, except perhaps for Patrick and Bridget. Even in Gaelic-speaking areas, it seems like you would have never found a name like Sean or Seamus in that period or perhaps for a period going back even earlier.
Since much of the society was still illiterate, I have wondered if a name like John may have been pronounced like Sean, since that is its equivalent, but one of the last storytellers, speaking entirely in Gaelic had the name John, pronounced John.
One exception is the name Thade or Thadeus, which was often interchanged with Timothy. So. perhaps, there may be a small possibility that the man had another name, which was sometimes used in the place of Phelim. For instance, I notice a Peter Sheppard on the tithes, which roughly date back to that era.
But, of course, that would be a real longshot. More likely, Peter was his one and only name.
I would recommend looking for Sheppards on the Tithes and Griffith's Valuation though, since they date back to closer to that era. Though, if he were a laborer, he may not have appeared on them. It could be he was of a poorer class if he emigrated to England.
Anyway, if you do zoom in on a parish record which survives with the name Phelim, I would say it is close to a sure bet, even if you don't straight away find Margaret.