How does one explain consistency within phenomena if the mind generates phenomena?
I too had this question for a long time. Then I read Gil Fronsdal's translation of the Dhammapada, which begins (emphasis mine):


  All experience is preceded by mind, 
  Led by mind, 
  Made by mind.


This use of the word experience, where phenomena is often used, is much more accessible. Remember, the Buddha did not say "all phenomena is made by mind"; he said "manopubbaṅgamā dhammā manoseṭṭhā manomayā". To say that much can be lost in translation would be an understatement.

I prefer Gil's translation of experience because it fits with what makes sense. It's not everything that exists in our mind, but how we experience everything. 

Consider a simple example. If you and I stand beside one another and together look at a houseplant in front of us, we will both see the houseplant. It's not that our minds are simultaneously (and coincidentally!) creating a houseplant that isn't really there; the plant is a real thing that exists in the world. But our minds will experience it differently: we'll interpret different shades of green, we'll consider the scent of the soil uniquely, and we may even have different emotional responses based on any memories associated with this particular kind of plant. The plant wasn't created by our minds, but every aspect of how we experience the plant was.

And remember the broader point that the Buddha was was making in that opening chapter, which continues:


  Speak or act with a corrupted mind, 
  And suffering follows 
  As the wagon wheel follows the hoof of the ox.


The point wasn't that everything we experience comes from our minds, but that because the mind plays a critical role in how we experience everything, the state of our mind set the stage for how (or whether) we will experience any suffering.