Get Touch touch phase began is grounded not working

i have no idea why my script is not working , it perfectly works with the up button , but with gui texture it doesn't.

using UnityEngine; using System.Collections;

 public class jumpdugmemovement: MonoBehaviour {
     
     private bool grounded = true; 
     public int jumpspeed = 350;
     // Use this for initialization
     void Start () {
     
     }
     void OnCollisionEnter(Collision other)
     {
         grounded = true; // collision with any object is grounded
     }
     void OnCollisionExit(Collision other)
     {
         grounded = false; // collision exit with any object is not grounded 
     }
     // Update is called once per frame
     void Update () {
         
     if(Input.touches.Length <=0)
         {
             //some code 
         }
     else
         {
          for(int i=0;i<Input.touchCount;i++)
             {
                 if(this.guiTexture.HitTest(Input.GetTouch(i).position))
                 {
                     if(Input.GetTouch(i).phase == TouchPhase.Began)
                     {
                         if (grounded == true)
                         {
                         GameObject.FindGameObjectWithTag("Player").rigidbody.AddForce(Vector3.up * jumpspeed); //then find player object and move up * jumpspeed
                         grounded = false;//jump        // set in air to grounded false 
                         }
                     }
                 }
             }
         }
             
     }
 }