Heh, with how the developers cooperate, you would never know there was competition.
But seriously, if you do want to fund Mobile Linux, buy a Librem 5. Purism funds dedicated GNOME/Phosh/etc. devs to work on making Mobile Linux a polish experience, and many of them also help to make sure it works on the Pinephone/Pinephone Pro. Heck, sometimes I think many of their employees spend more time helping out Mobian users on a Pinephone than they do Librem 5 users.
As much as I like Pine64 (I think making a $150 Linux Phone was an amazing idea!), they exclusively only fund the hardware development. Drew Devault has, IMO, a good overview of criticisms of Pine64: https://drewdevault.com/2022/01/18/Pine64s-weird-priorities....
I own both the PinePhone and Librem 5 USA, and I'm seriously impressed by the amount of work the Purism devs do for PinePhone users (who are the majority of the Phosh users).
I also have an L5 sitting on my desk that I am using full time, and have had it for several months by now.