Could be. I don't have an iphone to test but the app looks like it's working fine on my ancient ipad. There are so many different devices and set ups I just have to trust that the app vendor has one of each to test with.I think it is a phone app issue and not a browser problem. I am using a computer with Firefox and had no issues. A phone browser problem maybe though.
Hopefully once all of the updates are rolled out this will be fixed.