A huge problem arises any time you give out your phone number to any company. The potential of them giving out your number and you getting spam phone calls.
Over the last few years I've had to deal with this problem over and over again. The first step to try is to install spam blocking phone apps to your mobile device. Beware because many of these will try to charge you to use them or charge you once you block a certain amount of phone numbers. One free app I have found to be very helpful is called "Mr. Number". This app does a decent job at detecting and blocking spam phone calls on your mobile device. In the past, it had an option to hang up on them instantly but for reasons unknown they did away with that feature and now it simply routes the call to voicemail. So if by chance it is not a spam number the caller has a chance to leave a message.
Another tactic recently employed by spammers is "spoofing" local area phone numbers, or spoofing numbers with the same area code and exact same prefix as your own phone number. Spam call detection apps have a tougher time identifying spoof numbers as spam so you must use another option to block them. But block them you can, at least on google/android devices. Simply go to your phones settings>call>"Decline and reject calls" option.
From here, there are a few options you can use. You can select the option "decline with a message", which I've never used. Reject all calls from private numbers, which I do use. Then finally, the most advanced option "Reject calls from". In this option, not only can you enter exact phone numbers you wish to block but you can use the "starts with" option to block specific area codes or area codes+a prefix. This is especially helpful when you're blocking callers that keep calling from different numbers in the same area code or if they're spoofing your own area code and prefix. Just enter the beginning of the number into this field and set it to "starts with" and those calls are all instantly rejected from calling your phone.
I see numerous people online asking about how to block spam phone calls and this is what I've used myself and found to be most effective. I hope it helps others out there that might be dealing with this problem as well. If there's an app or a setting you've found to be effective please share it. Also, if you own an Iphone let me know what apps or settings you use on your device to block spam phone calls.