On Android phones, to set the initial page zoom level and disable the user controlled zoom, add the following code.

meta name=”viewport” content=”width=device-width; initial-scale=1.3; minimum-scale=1.3; maximum-scale=1.3;”/. Ensure that the scale have a min value of 1.3

For iPhone, add this code
meta name=”viewport” content=”width=device-width; initial-scale=1.0; maximum-scale=1.0; user-scalable=0;”/