“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” An ice age version is:
 
“The ice age walks into a bar. The bartender says, ‘Why the long phase?’”
   
The pun is on the famous “Why the long face?” punchline of the “A horse walks into a bar…” joke.
 
“The ice age walks into a bar, barman says ‘why the long phase’?” was posted on Twitter on August 30, 2013. “The Ice Age walks into a bar. The barman says ‘Why the long freeze?’” was posted on Twitter on April 30, 2018.
 
     
Twitter
Glenn Burchnall
@FOSSESPARK
The ice age walks into a bar, barman says ‘why the long phase’?
2:55 AM - 30 Aug 2013
 
Twitter
Ian Davis
@id1om
An ice age walks into a bar…
Barman:  “Why the long phase?”
8:05 PM - 27 Mar 2015
 
Twitter
Caught Jester
@brucedon5
The Ice Age walks into a bar. The barman says “Why the long freeze?”. #1Pun #mondaymirth
7:44 AM - 30 Apr 2018