We use rightfax. It requires a server, but that server can be in the cloud. Ours is virtual on prem. Some like it, some hate it. I think a lot of the hate is because of the person who rolled it out. He doesn't work here anymore.
https://atechnologies.com/rightfax/rightfax-cloud/
Still better than the woman printing off a 100+ page patient chart, putting each page in a fax machine, then putting the output of the fax machine into a confidential bin.
I hope she doesn't work here anymore either.