I recently bought tplink archer c50 v4 and it only has eu channel selection (i.e. 36-44) but the problem is that my phone cant detect 5ghz network but my firestick and tablet can. Will installing openwrt give me more choices and increase the channel range?
Possibly, that depends on the individual hardware. Sometimes vendor firmwares don't offer the full channel selection, probably because DFS wasn't available early on during the development and they never bothered to update their SDK afterwards.
Installation is not simple. You need to make a file by combining part of the stock firmware from the TP-Link website with the OpenWrt sysupgrade file.
Since the stock firmware is copyrighted, redistribution of such a file is legally questionable, so it is not posted by OpenWrt. If you scroll up the page to the other section about the V4 there are links to some third-party files.