Welcome tot he Fido community!
you can login to you account click on the number associated with the lost device and you should see the option to report lost/stolen device.
Once you block the phone you might not be able to trace it, depending on which phone you have and if you had location tracking enable you might be able to locate the phone, For Apple device see here for Android device see here.
Welcome to the Community!
If you have device protection on the line on which you were using the device that was lost/stolen, the Device Protection plan allows you to make a claim with Asurion, here, for a like-for-like or comparable replacement, however, lost/stolen coverage is not covered in Saskatchewan, Québec and Newfoundland, so, your coverage for this type of scenario will depend in which province you live in.
If you are living in a province where this is covered, Asurion will charge you a Service Replacement Fee via credit card for your replacement. The exact replacement fee will depend on which device you were using. You can check out more details on this on the same page where you can make a claim.
If you make a claim, the lost/stolen device can also be blocked from future use with any wireless provider in Canada.
Hope this helps!