I tried to call someone on the duo on my iPhone. the person I was calling his video get stuck all the time but I can hear the voice clearly. so I wanted to know that does FaceTime work on an iPhone
I looked it up and the best I can find is the video call quality is dependent on the coverage area of both devices. One thing I did notice was Duo has a very good rating across platforms and while not as good as Facetime to Facetime for Apple users Duo to Duo even from iOS to Android is rated very highly.
I guess the only advice that could be given would be to check signal strength before making a call, it won't tell you what the recipient's signal is like but it may help you gauge if quality issues are on your end or theirs.
PS Nomenclature can get tricky especially when talking about Apple to Android. I understand you calling it Facetime, even the video is labeled Facetime, it's like calling all adhesive strip bandages Band-Aids. In this case it's just a video call or perhaps a Duo call since that's the app being used.