Hi, I’ve purchased the Plyr Video Player and it works great, however I don’t see the icon to expand the screen size when trying it from my iPhone.
Please accept our apologies for the late reply. 
The full-screen option is not available on IOS, unfortunately. However, you can disable the ‘playsinline’ option within the plugin element. This action will prompt the video to automatically play in full-screen mode on iPhones.
Let me know if you have any further questions or concerns.
Best regards,
Gulce