Website Code Audit & Performance Boost

I have a live business-portfolio website that feels sluggish and breaks layout on some devices. I need a seasoned developer to dive into the existing codebase, spot what is slowing us down, and return a site that is fully responsive and noticeably faster... (Budget: ₹1500 - ₹12500 INR, Jobs: CSS, Frontend Development, HTML, HTML5, JavaScript, Node.js, PHP, Web Development)