I use the Feedly template.
https://yikyakclone.bubbleapps.io/
When I post in Safari on my iPhone, the input form zooms in and out of the screen.
Is there any way to solve this problem?
Hello, @oyogemasen. Thanks for reaching out.
Let us please investigate your request with our dev team. I hope we can find a useful solution in this case. The investigation might take some time so please be patient 
Thank you for understanding 
Regards,
Kate
One thing - when you scroll the browser page a bit, to hide the navigation bar and decrease the URL field (the upper part of the browser) and click on the input field, in attempt to write the post, the keyboard appears and the input form does not jump too far away out the screen.
Watch from 20 second - Safari screencast.
Yes, it is not quite a comfortable solution, but can do the trick 
Regards,
Kate
Just wanted to inform you that our dev team has tried to fix this issue with the popping up multi-line input field.
Unfortunately, it is not possible to fix it completely, because the multi-line input filed behavior is happening due to the iOS browsers feature. We have fixed the zoom when you’re clicking on the input field and the keyboard appears - so the input field is visible on the screen (you can check it if you create new app, using this template as a base).
Anyways, to reduce the UX damage, I can suggest you follow my previous suggestion - to hide the browser’s nav bar and then click on the input field.
I hope it will be at least a bit useful
Regards, Kate