Many modern mobile browsers will detect telephone numbers in your content and automatically convert them to links that recipients can click.
You can also manually setup links to telephone numbers using the tel: scheme to ensure they are always enabled for recipients to click to call.
To insert a link to a telephone number:
Go to the Content step of an in progress campaign.
Click into the editable area, and highlight or select the text or select the image you want to link to. Then, click the Create Link icon in the toolbar.
In the URL field, enter "tel:" (excluding quotation marks) followed by the international dialing format for the number: the plus sign (+), country code, area code and number.
While not required, you can also separate each segment of the number with a hyphen (-) to help ensure better auto-detection.
Click the Create Link to URL button.
You can test this on your mobile phones, which should present you with this