I think it has to do with our tendency to overcorrect spelling rather than use the simpler ones (at least when the native speakers comment here). I believe it's exploited in etymology - i.e. even literally authors made errors in spelling but these are thought to come mostly from trying to be more correct than neccessary

For me, while I had often heard and used "faze" in conversation, I seldom saw it in writing. Early on my mind got comfortable with the bogus idea that it shared etymology with "phase", and so I assumed they were spelled the same.