I think you are clutching at a very thin, possibly non existant straw here.
What makes you think that this William and Harriet Phillips (not exactly an unusual name) with their sons George and William, are the same people as a Thomas and Harriett Phillips who have a son, Joseph?
Do you have other evidence?
If not I would forget this family for the time being, and go back to finding your Thomas, Harriett and Joseph on the censuses