One phone / Few accounts

Yes, you can. Wait a minute i will find an article about that.

EDIT: Argh, i've seen it yesterday, but can't find now
EDIT 2: Here it is:

Can I share my phone number between multiple accounts?

Yes. You may use the same phone number on multiple accounts. You may enable Steam Guard Mobile Authenticator on multiple accounts on the same phone by logging in to each account within the app and following the procedure to enable the authenticator on each account. The app will provide codes for all accounts regardless of which account is currently logged in to the app. Accounts with the same phone number may be treated as the same identity with respect to the Steam Subscriber Agreement, policies, or restrictions.