Spire 3.9 changed the Sales Order contact on the Main screen. It has been replaced by separate Buyer and Receiver contacts, each with their own respective phone and email information, which can be set to default to the contact type set in Company Settings.
To set which Contact Type that you would like these to default to, please go to Edit > Company Settings > Sales Orders, Orders, Contact Defaults.
Set the desired Contact Type for Default Buyer and Default Receiver and Save. 
Spire will now automatically fill the Buyer and Receiver Contacts on new Sales Orders, if contacts exist for the customer on the Sales Order, if they exist.