You can find the best channel to use using one of these techniques: https://www.howtogeek.com/197268/how-to-find-the-best-wi-fi-...

Although, that article says you need a jailbroken iPhone to find the best wifi, it is possible to identify high traffic networks with your iPhone using the Airport Utility - https://forum.music-group.com/showthread.php?6603-TIP-Choosi...