Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
If you mean GNU/Linux - no. But you can buy a phone that supports Lineage OS. It's Android distribution, so you will have everything you used to have on your phone and the OS will be fully FOSS. Or even maybe you current phone is already supported. Check their website.
Thank you. This seems to be the best option at the moment. Right now I’m stuck on iPhone which I bought without realizing how restrictive their OS was. However I don’t have the budget or interest in buying a new device currently, so I’m just keeping an eye on my options.