It is always scary to try a different strategy. What if the phone calls stop? If you are afraid of reduced traffic on your website, you can consider slightly reducing your paid search campaign and invest in your content at a smaller scale. This will allow you to transition your call traffic slowly until your organic ranking improves.
The good thing about paid search is that you can always turn it on or off depending on your activity. If you are inundated with calls, you can always reduce your adword budget. If you are not getting any calls, you can increase your budget.
While you are adjusting your budget, you can set aside an amount to invest in your content so that you improve your organic ranking over time.