sforce.opencti.runApex() can be to run or execute Apex using OpenCTI in Salesforce.

Sample Code:
Apex:

global class OpenCTIController {

    webService static String fetchContacts( String strPhoneNumber ) {

        List < Contact > listContacts = new List < Contact >();
        listContacts = [
            SELECT Id, Name
            FROM Contact
            WHERE Phone =: strPhoneNumber
        ];
        String JSONString = JSON.serialize( listContacts );
        return JSONString;

    }

}

Open CTI JavaScript:

sforce.opencti.runApex( {
    apexClass : "OpenCTIController",
    methodName : "fetchContacts",
    methodParams : "strPhoneNumber=1234567890",
    callback : function( result ) { console.log( 'Result is ' + JSON.stringify( result ) ) }
} );

Output: