By default, the default phone number country code is US Country Code (+1) and the default time zone is GMT/UTC.
To edit the default country code for your event website, go to Setup > Registration and then click on the Advanced tab. Then scroll down to edit the Default Country Code.
To edit the time zone for your event website, go to Setup > Event Details and scroll down to edit the Time Zone.
Editing the time zone is important if you plan to use the Add to Calendar button at the end of event registration.