Would help to know the phone. And the hardware. You could have a different dac, codecs.... You could have a bad port or something.

Usually people are not able to tell the difference between consumer facing dacs in phones, unless you're using really high-end stuff and using maybe LG's quad Dac.

But we just don't have enough information about your hardware. And use case.

Is it two copies of the same phone?

If so, they should have basically identical sound, but it's possible one of them has replaced parts or the port could be messed up or something.

I don't know. There's infinite variables so we need more information.