Hi @GSH,
Could you please share a screenshot of your flow's configuration?
Do you use the "When a new event is created" trigger of Outlook connector within your flow?
Further, do you want to extract the email address from Body of Outlook Calendar event?
The Microsoft Bookings connector is not supported in Microsoft Flow currently, if you would like this feature to be added in Microsoft Flow, please submit an idea to Flow Ideas Forum:
https://powerusers.microsoft.com/t5/Flow-Ideas/idb-p/FlowIdeas
I suppose that you use the "When a new event is created" trigger of Outlook connector within your flow, is it true? I have created a event in my Outlook calendar, the body of the event as below:
I have made a test on my side and please take a try with the following workaround:
- Add a "When a new event is created (V1)" trigger.
- Add a Condition, left input box set to Subject dynamic content of the trigger, right input box set to FlowTest, within middle drop down, choose is equal to.
- Within "If/yes" branch of Condition, add a "Html to text" action, Content field set to Body preview dynamic content of the trigger.
Add a "Compose" action, Inputs set to following formula:
add(indexOf(body('Html_to_text'),'Email'),7)
Add a "Compose 2" action, inputs set to following formula:
indexOf(body('Html_to_text'),'Phone Number')
Add a "Compose 3" action, inputs set to following formula:
substring(body('Html_to_text'),outputs('Compose'),sub(outputs('Compose_2'),outputs('Compose')))
Add a "Send an email" action, To field set to output of "Compose 3" action.
Image reference:

The flow works successfully as below:
Best regards,
Kris