Hello lewis,
By default theme doesn’t have Phone number or text options on the date and time section. We would like to recommend you two solutions.
1. Create child theme and customize the header section, you just need to edit the acmethemes/hooks/header.php file of the theme folder
or
2. You can try Header Advertisement section and can put your phone number or other text on Google Ads Part and select Adsense on Advertisement Show Option. It will show phone number on header but no at the place of date and time.
Best Regards!
Acme Themes