What is correct: touch base, touch bases, or touch basis?

The correct expression is “touch base”. It means “briefly talk with someone in order to stay in contact or check something.”

“Touch bases” is a mistake (the word “base” is always singular in this expression).

“Touch basis” is also a mistake  (where someone wants to incorrectly use the plural of “base” and also misspells it).

The QuillBot Grammar Checker can help ensure your writing is free of spelling mistakes.