Taxi

Of course, taxi tend to be where taxis are needed.

OP said “We will not have a phone.”

You do not need a phone when you are at train stations and airports! The taxis are lined up waiting for you.

Will not have a phone to book.

Guess OP means no possibility to call.

Tip: German ICE trains and larger train stations including Bonn with Deutsche Telekom HQs have wifi (in Germany correctly called WLAN). So you can use the myTaxi App with a smartphone.

Tip 2. In Munich center the ride sharing app CleverShuttle is a real good alternative.

Munich: exit the train station on the north side (coming from your train to the left); there are usually numerous taxis waiting.

At Munich Hbf (pdf map) you will find taxis in front of north and south exit. It makes sense to be aware where you want to drive with taxi.