Thank you for your post.
This appears to be an iOS issue. If you launch Safari and double-tap, it will zoom in. If you are on a text object or non-blank area, it may jump around and not zoom out.
Using the Sample Inventory file, go to the Record Detail layout (default). In the lower right area, double-tap in the gray area. You will be able to zoom in and zoom out every time. Now, if you double-tap the field labels in the middle of the layout (That is, In Stock Level, Reorder Level, Catalog Item, Etc.), it will zoom in as expected. However, double-tapping will probably center the field label to the middle of the display and not zoom out. Find a blank area and double-tap again to zoom out, or use a pinching motion to zoom out.