Mobile devices such as iPhones often need to be told not to zoom the whole page. There’s a good description here.
Use this in the head to stop zooming occurring:
<meta name="viewport" content="width=device-width, initial-scale=1">
Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.