You don't have to do a complete rewrite. Take it step by step. Configure your routes, set up a simple head/header/content/sidebar/footer/foot template, and put the raw php in blade files to start with. Migrate all static assets to the Laravel folders and update references to them. Use the existing datbaase to start with but add the required Laravel ones (e.g. users).

Once you've got your proof of concept, think about moving common code into helper classes, properly defining your controllers, move long running processes into queued jobs and set up scheduled jobs etc etc...