Any plans for mobile/responsive website?

I don't have a mobile device, but last few times there was a thread asking for it, most people claim that the website functions perfectly without an app.

Other than than, you can use unofficial apps like this one: https://www.steamgifts.com/discussion/Zpeq5/steamgifts-for-android

Probably not. But you can use Steamgifts for Android app made by fellow steamgifter. It's available on Google Play.

I've been using it for over a year and it works well. Unfortunately you can't create discussions with the app.

It works just fine for me. It just feels weird at first but you get used to it. Believe me, I've been using only the phone for the past few months.
Nokia 3 here.