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The RC records for Castleconor RC parish start in 1854 https://registers.nli.ie/parishes/0743 so when I searched on the subscription site Roots Ireland no Thomas Phelan records were available in that parish.
I also checked the 1858 Griffiths Valuation head of household listing for Castleconor civil parish and there were no Phelan records. https://www.failteromhat.com/griffiths/sligo/castleconor.htm
I assume you do not have the names of his parents or any siblings.