Hello, @Raeh60
You’re right. There is no Phone Number field to add in a document as you have for email, title, name and others.
A suggestion: you can use the Pre-Fill tools when adding field to the document. On this case, you could add a Text Field for each recipient, type in the advance the Phone Number for each one and place in the positions where you would like they show up.
Another approach, when you send an envelope to a recipient you can select SMS as the delivery method together the email method. You will need to type yours recipients phone number to them get the notification to sign via SMS.
On this case, it’s possible to run a Report for Recipients Activity and add the Recipient Phone Number used in the delivery method.
I hope that helps.
Alexandre