PHP - Store a function without executing it

I want to store this:

strftime('%Y-%m-%d %H:%M:%S','now', '+3 day')

in a variable without having it being executed.

I want to insert this line in a SQLite database but the "strftime" is already a PHP function and it throws an error telling that this line is "false".(Which is true because executed in PHP)

But in SQLite, I know that it is a totally right statement.(I did execute it directly within my database and it gave me what I want)

Any help would be appreciated.