My philodendron and birds of paradise started out good. Issues 9 months in.

Hello!

My philodendron plant aka Congo Rojo. The plant started well, it was nice and shiny when I purchased it. Anyway, lately I’ve been seeing these dots appear on the leaves and they look concerning (see image). The leaf that came out a week ago is much smaller than the previous leaves. From what I know about plants, that is not a good sign. The plant gets a lot of light as you can see from the pictures and I only water when it needs it. Any suggestion?

My birds of paradise have a similar story. The bottom leaves were yellow and dried so I had to cut those down. The other bottom ones are on the way. The new leaf growth has slowed down significantly.

Let me know if any more information is needed.

A few things -
I think your bird of paradise needs to be repotted into a larger pot. The one it's in looks too small. If there are a lot of roots that you can see if you pull the plant out and some are circling, then it's rootbound and needs a larger pot.  When you repot it, unbind those circling roots, remove any that are dead or unhealthy, and repot it in good soil in a pot with holes in the bottom so it gets good drainage.  As for the philodendron, is in a pot that has drainage holes? If not, that definitely needs to be repotted as well.
Secondly, philodendron need only medium to low light.  If it is in a really sunny location, it should be moved to a more gentle location. Bird of paradise needs good direct lighting.
Both plants like moist soil but like to dry out some between waterings. Water when the top inch of soil is no longer damp, but do not let it dry out completely. When you water it, put the pot in the sink or outside and water until the water is pouring out the bottom.  (If the soil is actually totally dry, you may need to soak it in a sink of water.) Let it drain well, then put it back in its location.  
Whatever is causing the spots on the philodendron may be alleviated by the above, but they could be a fungal or bacterial infection that could spread.  If you can without damaging the plant, remove the leaves with the spots on them.
Good luck!