How do I play volume on the kasa app thru my iPhone? 

I have an old phone that I just run on wifi and use as a baby monitor thou I loaned it to the babysitter who was watching my son and on return it hasn't played volume on this iPhone from the app again yet plays volume for songs and movies on the phone no problem. So it isn't a speaker problem with the phone. I have tried adjusting the settings within kasa app under privacy and sensitivity and it just won't work thou will play sound picked up from the camera when I connect headphones or a Bluetooth speaker to the phone. It is just super annoying as I use to sleep with the phone next to my bed with the app open and could hear baby thru the night but now it won't work!! I've factory reset the settings on my phone, turned it off & on, deleted the app and downloaded it again, tried to change the settings both within the app and on general settings of iPhone, tried headphones (hence why I know there is still volume coming from the camera). If there any ideas or suggestions that would be appreciated as I'm at a complete loss!!!