I just use robinhood on my phone and it supports either share or dollar purchases

Quite a few do, you can find lists online pretty easy. I know for a fact Robinhood does but I think I had to be on a waiting list for that one. Be careful - most brokerages will limit the kinds of stocks you can buy fractional shares of, so if there's a particular stock you're eyeing make sure it's on the broker's fractional share list.