The checkmark does mean the call is verified by your cell provider. A verified caller is still able to call you and ask if you are selling your house or wanting you to donate to a charity, so yes it could still be considered spam. It does help to identify callers who have spoofed their caller ID or the number that shows has not been determined to be a legitimate number.
Many cell providers also have additional Spam blocking technologies. In some cases they just need to be turned on and other times it may be an additional service charge. For example TMobile has a service called Scam Shield that can be used for free and a premium service for $4/month that gives you more control.