Extremely weak WIFI but stong/normal over ethernet

I have been having a lot of issues with our ATT provided router recently. Whenever I try to use my phone over WIFI it constantly buffers, takes forever to load, and sometimes I have to completely shut off the WIFI and just use our data. My PC (In the exact same room that I am using my phone in, not that it matters since its over ethernet) gets our normal/expected 50 up/15 down Mbps but my phone is only getting like 1.5 up and down. I am not too far from our wireless router (maybe 35-45 feet max) what do I need to do to fix this? Also is it possible to use my own wireless router like the TP-Link AC1200/Archer C5? I also attached the speed test of my phone and PC.

Thanks in advance.

PCPhone