sforce.opencti.enableClickToDial() method can be used for Salesforce Lightning Experience Open CTI Click to Dial. 

Sample Code:

let callbackFunc = function( response ) {
    
    console.log(
        'Response Success value is',
        response.success
    );

    if ( response.success ) {

        console.log(
            'returnValue:', 
            response.returnValue
        );

    } else { 

        console.error(
            'Errors:', 
            response.errors
        );

    } 

};


sforce.opencti.enableClickToDial( {
    callback: callbackFunc
} );

Reference Article:

https://developer.salesforce.com/docs/atlas.en-us.api_cti.meta/api_cti/sforce_api_cti_enableclicktodial_lex.htm