All you have to do is launch your dialer and call 1244 with your Glo line whose number you want to check.
Just like you are receiving an activation code from Google, a voice will tell you your Glo Phone number and that’s it.
You can also check your phone number by visiting http://hsi.glo.com/HSISelfCarePortal/. Your number will be displayed at the top right corner of the website.