Hold down a touch input

Hi everybody, I'm making a basketball mini game for android

I need that while I'm holding Down the Button(represented with a guiTexture), the variable called "power" increases its value in order to give more power to the ball and when I release the button, it will throw the ball.

I think that is something like Input.GetButton but I don't Know to do it

so this is my code

 function Update () {
 
 
     for (var touch: Touch in Input.touches)
     {
         
         if(touch.phase==TouchPhase.Began&&shoot.HitTest(touch.position)) 
         {
             power+=2*Time.deltaTime;
             if(power>500)
             {
                 power=500;            
             }
             Debug.Log(power);
         }
         
         if(touch.phase == TouchPhase.Ended && shoot.HitTest(touch.position)) 
         {
             if (waitTilNextFire <= 0)
             {
             ballContainer =Instantiate(ball,ballSpawn.transform.position, ballSpawn.transform.rotation);
             ballContainer.rigidbody.AddForce(0,6,1*power*Time.deltaTime, ForceMode.Impulse);
             waitTilNextFire = 1;
             }
         }
 
     }
     
     waitTilNextFire -= Time.deltaTime * fireSpeed;
 }

thanks in advance