When messaging a friend in WhatsApp recently I spotted that, when selecting text, the floating buttons let you bold/italicise/etc text (since seems like a feature WhatsApp added themselves since I haven't seen it anywhere else...):
Since WhatsApp also uses markdown-esque styling (ie using asterisks for italics) this feature can be pretty directly applied to the Joplin mobile app.
This would also be FAR more convenient than having to go into my punctuation portion of the keyboard every time, not to mention, it saves having to memorise what symbols lead to what markup!