Phone number /Top header on mobile only

Dear Enfold support,
not sure what I’m doing wrong, as the topic suggests, I’d like to show a phone number on mobile view and found these 2 code snippets:

/*mobile only phone*/
   @media only screen and (max-width: 767px) {
       #header_main {
           display: none;
       }
       #header_meta {
           display: block;
       }
   }

and

@media only screen and (min-width: 768px) {
.phone-info { display: none !important; }}

Both are not working for me :-(
Can you help please?

Best regards,
Stefan