Hi amargello,
As per my understanding, you could do below to add a follow-up step:
1. Click "+" to add a "If/then branches".
2. Click the branch tile, set the source to your Email, set the condition to "has been opened".
3. Click "+" button of Yes branch, add a phone call.
Final result:
You could refer to introduction about new canvas UI designer.
https://docs.microsoft.com/en-us/dynamics365/marketing/customer-journey
In addition, as you mentioned, UI of journey template is still same to the previous, because the new UI feature is still in early access,
template designer might be also upgraded to the new UI with the general availability in October.
Regards,
Clofly
