Asus VA279 connected to an iPhone

Hello! I have an ASUS VA279 and I was trying to use it with my phone. I couldn't turn the image to a vertical position but a friend had an Iphone. We tried with her phone and it worked. I bought an iPhone to be able to use it and when I tried the image didn't turn vertical, I called her and we tried again with her Iphone and didn't work this time. Any advice? I am a tik-toker and I am deaf, I need the large display to see properly when I am performing. Your help will be greatly appreciated.