You can use like following
$participants = fep_get_participants( $mgs_id );
foreach ( $participants as $participant ) {
if ( $participant == fep_get_message_field( 'mgs_author', $mgs_id ) ) {
continue;
}
$mobile = get_user_meta( $participant, 'mobile', true );
$msg = 'What you want to send';
wp_sms_send( $mobile, $msg );
}