If you cannot use your fixed phrase, these reasons below are considered.
・The box [Replace sentences entering] is empty. ・[:] is full width
The box [Replace sentences entering] is empty
In order to [Replace sentences entering] in [Manage fixed phrase], the box needs to be checked. Here is how you can set and check.
(1) Click on the setting button on the upper right of the management page. 
(2) Click on [Manage fixed phrase] on the left side of the screen. 
(3) In the section [Option], check in the box [Replace sentences entering]. 
(4) Click on [Update].
[:] is full width
When using fixed phrase during the chat, you need to enter [:] and alphabets in half width. If you enter it in full width, it would not function.