Holy Zohar text. Daily Zohar -41.

The three straps of the Tefilin (Phylacteries) are for Netzach, Hod and Yesod.
Netzach and Hod are the two straps that comes from the head. Hod is the left and short strap and should reach the heart. The strap of Netzach is on the rights side and should reach at least to the middle of the body.

The Tefilin house of the hand should point to the heart to draw from the upper levels through the left column and with the strap of Yesod it continues to the middle finger of the left hand to manifest the light with positive action.

מקור הקטע: הקדמת תיקוני הזוהר עם פרוש מעלות הסולם (רבי יהודה צבי ברנדויין זל) פסקה 199