Is it because yur 'keyboard" is over laying the area you would type?
The forum works fine in general, some people report issues with chat including the above and was issue for me too- because I had the settings on phone turned up larger because my eyes are not great. Making the font sizes and keyboards a larger causes the issues in chat and some areas where you would type due to the increased size of the keyboard. 74% of our users access with a mobile device however, so since the vast majority are using a mobile to access us , it does seem to be an issue with individual phones/browsers/settings as opposed to a problem overall and when we look at the analytics where different browsers "grade" your site for user experience/user friendliness for the site we score extremely high on mobile (higher on mobile than desktop actually).
That is not at all to say you don't have an issue or we don't care- it is just explaining why the settings are where they are for the site- and that we cannot really make adjustments from the site end- it is set to where it is most accessible for most people. I am very sorry it is not working well for you. If you can attach a screen shot of the issues, and tell us what phone, operating system , browser (and browser version) I can try to trouble shoot it more specifically to help make it work better for you.