Stolen phone

Yes, they will be able to use the phone. From the article below.

Turn off Activation Lock on a device

1. In Find My iPhone on iCloud.com, click All Devices, then select the device you want to erase.
2. If you don’t see All Devices, it’s because you’ve already selected a device. Click the name of the current device in the center of the toolbar to access the Devices list, then select a new device.
3. Erase the device.
4. Because the device isn’t lost, don’t enter a phone number or message.
5. If the device is offline, the remote erase begins the next time it’s online. You receive an email when the device is erased.
6. When the device is erased, click Remove from Account.
7. 
8. All your content is erased, and someone else can now activate the device.

Remove a device from Find My iPhone on iCloud.com - Apple Support

angel_socola wrote:

My phone was stolen. I've already erased it remotely but haven't removed it from my account yet. If I do it so, will the thief be able to use it as new?

no