I am needing to add a contact number to the check out process and would like to know if you have any suggestions on how I could do that?

In other words, when the buyer is reviewing the shopping cart, there would be a field requesting them to enter a phone number so we can contact them if needed to finalize their order.

You would probably need to do that via PayPal, I would think that would be expected as default myself, but check to see if there is a setting there to ask for it on each order. Otherwise you'll need to add a separate form whoch could be a bit messy just to grab a phone number.