PHP 5.6 Upgrade & Migration

My current site, https://solenoidvalveindia.com/, still runs on PHP 5.6. I need the entire codebase brought up to the newest stable PHP release, moved to a fresh hosting environment, and cleaned of the template-level problems that stop our email and SMS gateways from firing correctly. The upgrade must preserve all existing functionality while eliminating deprecated calls and library conflicts, so every page, form, and database interaction works exactly as it does now—only faster and more secure.

There are a few small enhancements I would like to bolt on once the platform is current, but the immediate focus is:

• refactor the code for PHP 8+ compatibility,
• configure and test the email/SMS gateway scripts after the refactor,
• copy the finished build to the new server and point the domain,
• verify that every transactional message (both email and SMS) sends successfully from the new host.

I will provide cPanel/SSH access for both the old and new servers plus gateway credentials. Please give me a brief outline of your approach, the key steps you’ll take to spot and squash deprecated functions, and the timeframe you need to complete migration, regression testing, and launch.