TL;DR

Old text messages with one-time auth codes were leaked (not yet sure from exactly where). The leaked messages were not tied to any phone numbers. Even if they were, they would be useless since they only last for 15 minutes and Valve sends you an email for any account changes anyways.

You do not need to change your passwords or phone numbers as a result of this event.

You may have seen reports of leaks of older text messages that had previously been sent to Steam customers. We have examined the leak sample and have determined this was NOT a breach of Steam systems.