Question on Tefillah:
Why do we only say ‘Ki shem Hashem ekra havu godel lelokeinu’ (at the start of the Amidah) in the Minchah service and not in the Shacharis or Maariv services?
We only say this for minchah, because it is not actually part of the Shemoneh Esrei prayer, and therefore we cannot say it in places where it is forbidden to make an interruption before the Shemoneh Esrei. Only at Minchah, where there is no prohibition of making an interruption, can the addition be made.
Note that it is likewise made in Mussah, and in Ne’ilah on Yom Kippur.