It's up to the organiser whether they provide a phone number with their request, so you will find that certain requests will not have a number.
Of course, you can request a phone number when you send your quote so feel free to send them a follow up message asking for this.
You can check if a customer has left a phone number before quoting by:
Clicking into the request
Navigating to the event details
If the customer has left a phone number, you will be able to preview the first 3 numbers followed by a series of asterisks (e.g. 077********). This will appear at the top of the event details under the customer's name.
If the customer has not left a phone number, you will see "No Phone Number Provided" in this space.