Sorry for the loss.
His phone was a business phone and we returned it. How can I log on using his apple id,
The company has already deleted his work email address. This is done as soon as he is not work any more for the company.
An deleted work email address, it is no longer valid, it simply no longer exists and it no longer works.
You are not be able to sign in that email work email address because it is no longer exists.
if I do not have his phone to receive verification code.
Only the company has that number, not sure if that number has been used by someone else.
Get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service
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If you have other Apple devices registered with his Apple ID, see -> How to request access to a deceased family member's Apple account
How to request access to a deceased family member's Apple account - Apple Support