I tested this behavior in the web client & OPAC for both Chrome (60, 64 bit) and Firefox (54, 32 bit) as well as in the XUL client.
In all cases, the following happened:
If I click submit with the phone number box checked & field blank, I get a popup asking me to fill out all required fields & the field highlighting changes to yellow.
If I uncheck the phone notification I am able to click submit and the hold is successfully placed.
I'm not seeing any differences in behavior if I come from "place another hold for this title" -- it's working as expected there too.
3.0 beta
I tested this behavior in the web client & OPAC for both Chrome (60, 64 bit) and Firefox (54, 32 bit) as well as in the XUL client.
In all cases, the following happened:
If I click submit with the phone number box checked & field blank, I get a popup asking me to fill out all required fields & the field highlighting changes to yellow.
If I uncheck the phone notification I am able to click submit and the hold is successfully placed.
I'm not seeing any differences in behavior if I come from "place another hold for this title" -- it's working as expected there too.