I dont have an iPAd to hand to test this but I know that Safari likes to change phonenumbers into links which would override the current CSS which makes the text white.
You will need to change the CSS to ensure links remain white.
Try adding this CSS to your theme’s style.css:
#main-site-caption #number {
color: #fff;
}
If you cant contact the developer you may be able to add this yourself.
You will need access to the WordPress dashboard, in the menu on the left click ‘Appearance’ then ‘Editor’ from here open the style.css file (will be listed on the right along with other theme files) and just add this to the bottom of the file.