You must first apply to the accommodation offer. On each ad, there is a blue button "being called back" or "see the number". Click on it to send a 'push' to the manager (who will contact you) or get access to the phone number of the owner of the housing (the number is only available if the owner chose to display it).
If the owner decided not to show the phone number, you'll need to wait for a reply before asking for the contact informations. If a landlord is interested by your profile, you'll be able to chat through the "Message" section of your account.