Estimator, coverage and the request form pair controls with their result so nothing needs scrolling to compare.
Above 640px the anchor nav returns and sticks to the top, with the phone number held to the right edge.
Text never stretches to the full window on a 27-inch monitor; the measure stays readable and the page keeps its left edge.
One page serves both sizes. No separate mobile site to keep in step, no redirect, nothing to forget to update.