Try something along these lines:
Code:
Private Sub TextBox1_GotFocus()
With TextBox1
  .AutoSize = True
  .Left = Range("B1").Left
  .Top = Range("A356").Top
  .Width = 590
  .EnterKeyBehavior = True
End With
End Sub

Private Sub TextBox1_LostFocus()
With TextBox1
  .EnterKeyBehavior = False
  .Top = Range("A356").Top
  .Left = Range("B1").Left
  .Width = 590
  .AutoSize = False
  ht = .Height
  Debug.Print ht
  .Height = Application.Max(171, ht)
  Range("A356:A375").RowHeight = (.Height / 20)    ' + 0.5
  .Height = Range("A356:A375").Height
  Do While .Height < ht
    Range("A356:A375").RowHeight = Range("A356").RowHeight + 0.25
    .Height = Range("A356:A375").Height
  Loop
End With
End Sub