Alternative to double tap gesture

Hello,
I currently use an ipad mini 4, but a family member let me borrow their phood so I could practice answering and making calls using Voiceover. They have an iphone 6s. Sometimes the double tap gesture works for m"* sometimes not. I can get the two finger double tap to answer a call, but it does not seem to work when hanging up a call. Therefore, is there an alternative to double tapping the screen? If so, what is it and does it work for gestures that require two or more fingers? I have the same trouble on the ipad; sometimes double tap works, sometimes not. Is it semething I am doing wrong? Your thoughts are greatly appreciated.