Ok so I looked into this and amazingly enough the only way it seems that you can access the alt text on Safari iPhone is to actually turn on VoiceOver in Settings>Accessibility - which most vision impaired users (those would need alt text at least) would use anyway in order to navigate the OS, but sucks if you’re testing. When VoiceOver is activated, and my comment is read out (you can try it by selecting it with the image in Safari), VoiceOver does indeed read the alt text.
You won’t have the same issue with Chrome on iPhone, you can long press and see the alt text.
Ok so I looked into this and amazingly enough the only way it seems that you can access the alt text on Safari iPhone is to actually turn on VoiceOver in Settings>Accessibility - which most vision impaired users (those would need alt text at least) would use anyway in order to navigate the OS, but sucks if you’re testing. When VoiceOver is activated, and my comment is read out (you can try it by selecting it with the image in Safari), VoiceOver does indeed read the alt text.
You won’t have the same issue with Chrome on iPhone, you can long press and see the alt text.
All good. Thanks for looking into and figuring how it all works. And patiently explaining it all