Please describe how can I merge the Shipping and Payment steps of the order creation steps into one step?

I need to make the ordering process as simple as possible, because I have no shipping, but the "Onsite pickup" only. So the users have to only put their contacts (Name + Phone, even without email) and choose the onsite location (a radio list with the pickup places), and that's it, they will pay onsite too.

So, the only required fields to ask are only three:

1. Name

2. Phone

3. Chosen pickup place

And that's it!

I can't find a way to simplify the current pretty complex multistep order submission process in Odoo to make it one-step and simple like described above. Please give me some hints on how to do this? Thanks!