iPhone Wi-Fi disconnecting when I watch YouTube
Try to troubleshoot, it sounds like you have some problems, which are not related to the application itself.

Some ideas to check:


check the WiFi signal, how many bars do you see in the place where you normally watch it, it could be you covering the signal with someting (phone stand, hands, walls, furniture, etc), and signal goes weaker, until totally lost;
try to connect to another WiFi access point, with the same video application or even the same video clip, and check if you experiencing the same issues;
check the settings on your WiFi router (or data plan limitations with your provider), may be it has some bandwidth limitation, and when you watch videos which are heavy on traffic - it just cuts the bandwidth, or something;
connect another phone of your friend, preferably with the same phone model to the same WiFi access point, to understand if the issue is connected to specific phone, or to specific access point.
try to reboot WiFI router, and the Iphone, to see if this will help as well, it could be some temporary hardware/software glitch.
if your WiFi router has several WiFi bandwidths: 5GHz and standard - try switching to one mode, without 5GHz, sometimes it helps, as phone is shifting between them and might loose the connection.


Hope this helps you to troubleshoot!