This is Elias with Shopify Support. Thank you for reaching out.
I understand you're looking to add a phone number next to the cart icon on the desktop version of your Venture theme. I've taken a look at your store and I can see that you have the phone numbers listed in the footer at the moment. Does the placement in the footer not work for the store? Or, were you looking to make the phone numbers clickable in the header?
I was able to find a couple of threads that offer different solutions for adding a phone number in the header - Adding a clickable phone button or phone number to my header/homepage and Add business phone number to the header of website. However, since you only want to add this on the desktop version, then this may be something that our Theme Support team can help with exploring.
As part of our design policy and if your store is subscribed to a plan, you're eligible to use the complimentary design time for customizing your theme. Though we're not able to provide account-specific support via the Shopify Community Forums at this time, we'd be happy to continue assisting you through live chat, email, or callbacks. Please visit Shopify Help Center and log into your account to create a support request.
Also, since it seems your store is almost ready to launch, do you have a marketing plan for your store yet?