My personal opinion is that you can't claim any deduction for phone or internet service as a business expense if you have a flat rate plan. You would be paying the same no matter how much business use you have, so you can't fairly attribute part of the cost to business use. I know that some authorities view the situation differently and tell you that you can deduct a percent of your phone and internet service based on the percent of business use. Even to do that, you need activity logs or other proof that show the percent of use. (You would need to meter your use, or get your phone bill and divide up the data transactions by use, or find some other way of actually proving your percent of use.) If you can prove the percent of business use, then you can deduct what you pay even if the bill is in your spouse's name.
The purchase of phone equipment can only be expensed, deducted or depreciated if you actually own the equipment. Because phones are "listed property" you can only expense the item if you use it at least 50% for business and can prove it with logs.
If you really want to deduct phone and internet as a business expense, you should get a separate phone and billing account for your business.
