How can I log into a deceased spouse's iPhone using their old iPhone?

Hello!

Please see if this Support Article provides any helpful info: How to request access to a deceased family member’s Apple Account - Apple Support.

I'm sorry to hear about the passing of your husband. My condolences.

Have a great day.

Hello~ Nice to have you back!!

~Katana-San~

~Thank you Katana! Nice to see you too~ 😊

Hello~ Keep putting in the good work as I would love to see you at a Level 6. Take care my friend.

~Katana-San~

Just to clarify on your original question....How can I log into a deceased spouse's iPhone using their old iPhone?

I'm sorry, but this is not possible.