In this rule

Historical Rules · 16 January 2016

Rule 110.5f

Official source text from the 16 January 2016 Rules release

A token that’s phased out, or that’s in a zone other than the battlefield, ceases to exist. This is a state-based action; see rule 704. (Note that if a token changes zones, applicable triggered abilities will trigger before the token ceases to exist.)

Find this number in the current Rules