Error 42601 when executing a stored procedure in C # with PostgreSQL

I am trying to create a method that executes a stored procedure that allows me to insert records in a table. However, I get an error preventing the method from running.

This is the code:

    public bool Insertar(string nombre)
    {
        try
        {
            NpgsqlCommand comando = con.CreateCommand();
            comando.CommandText = "EXECUTE Insertar @telefono";
            comando.Parameters.Add("@telefono", parameterType: NpgsqlDbType.Varchar, size: 10, sourceColumn: "5").Value = nombre;
            con.Open();
            comando.ExecuteNonQuery();
            con.Close();
            MessageBox.Show("se guardo");
            return true;
        }
        catch (Exception er)
        {
            MessageBox.Show(er.Message,"Advertencia");
            return false;
        }
    }

And the error I get:

  

42601: Syntax error near