There are several synonyms for the phrase "became obsolete," which means outdated or no longer in use. One synonym is "fallen into disuse," which implies that something was once popular or necessary but has since been replaced by something else. Another option is "outmoded," which suggests that something is no longer fashionable or relevant. "Deprecated" is another synonym, indicating that something is no longer supported or recommended. "Superseded" is also a suitable option, meaning that something has been replaced by a newer or better version. Ultimately, there are many words that can convey the idea of something becoming obsolete, and each one may be more appropriate depending on the context in which it is used.