How to monitor the movment speed of a 2D sprite

I am trying to get an enemy to follow the player when he gets to close, but I need him to flip between left and right but my only problem is I don't know how to monitor the speed of the enemy so I don't know when to tell it to flip, can someone please help me? here is my code: I do have a rigidbody2D attached to it so you can also use that.

public class FlyingEnemy : MonoBehaviour {

  private PlayerController player;
  public float moveSpeed;
  public float playerRange;
  public GameObject deathAffect;
  public int pointsOnDeath;
  public LayerMask playerLayer;
  private bool playerInRange;
  private Rigidbody2D RB;
  // Use this for initialization
  void Start ()
  {
      player = FindObjectOfType<PlayerController>();
      RB = FindObjectOfType<Rigidbody2D>();
  }
  
  // Update is called once per frame
  void Update ()
  {
      playerInRange = Physics2D.OverlapCircle(transform.position, playerRange, playerLayer);
      if (playerInRange)
      {
          transform.position = Vector3.MoveTowards(transform.position, player.transform.position, moveSpeed * Time.deltaTime);
      }
      if (RB.velocity.magnitude < 0)
      {
          transform.localScale = new Vector3(1f, 1f, 1f);
          Debug.Log("moving left");
      }
      if(RB.velocity.magnitude > 0)
      {
          transform.localScale = new Vector3(-1f, 1f, 1f);
          Debug.Log("moving right");
      }