Looking to improve gaming battle report filming quality, what do you recommend or where to start?

We have a small YouTube channel (a few 000 views per video) for recording battle reports like Warhammer, dropzone and other tabletop games. We currently do all of it with my old phone a Mate 20 Pro. The quality is ok, but tends to noticeably drop off over the length of filming, each video is a around 90 mins total of 8-15 shots. I assume it's overheating, it also tends to struggle if the room gets a little darker, we've mostly fixed this with lights but do still have a window that can affect the light level. We're looking to spend around £4-500 all in and don't mind looking at refurbished or something like that if it'll save us a bit. I'm not really sure where to start looking as it's a little bit niche what we're doing! If it can also take some great stills for overlay or display shots of models that'd be a bonus!

Any advice or pointers are very welcomed, thank you!