The officially approved method for writing and giving phone numbers is left to right, digit by digit, in groups of two, separated by a pause:
 

Sometimes Germans do not speak phone numbers digit for digit as prescribed. Even then, they typically group by twos:
 

Examples of Phone Numbers

• Vorwahl 4 - 0 - 4. Und die Nummer 6 -5 -7 - 8 - 9 - 1 - 2. Apparat 3 - 0 - 2. Verlangen Sie Frau Smith.
• Susi: Vorwahl 4-4. Dann 1-8-1 und 7-5-6 3-9 0-2.