Here's a compiled list of all the risky functions and actions that have been found along with their relevant issues. We will be updating this list as more risky actions come to our attention. Doing the following have a high change of phone-locking/disabling your account:

• bot.createDM (Discussion: Recommended way of using createDMs? #41)
• bot.requestFriend
• bot.joinGuild
• bot.setAvatar (Joining guild after using setAvatar function locks account #34, setAvatar phone locked my account #76)

And, of course, for most endpoints, abusing the REST api (not waiting adequately between requests) can get your account phone-locked/disabled. Ideally, try not to get rate limited in the first place.

edit: b5a92ca updates the headers and cookies - was able to join a guild and dm a user right after from 2 accounts (1 new and another 1-week-aged). Try reinstalling and seeing how it goes.
Note: don't set suspicious user agents. If you set a good user agent, discum should join (non massive guilds), dm, etc smoothly.