Electrical – What’s causing a bad response time of a phototransistor at 100 Hz

I am working on a project that involves communicating with LEDs. I need to be able to detect the state of a light source that is flashing at about 100 Hz. I am using the phototransistor that comes with the Arduino Starter Kit, but I am noticing that, while the phototransistor detects a difference between the high state and low state, this is very minimal. Is this simply because of the phototransistor's response time? If so, are there any other components (preferably inexpensive) that I can use to detect light from a source that is flashing at this frequency.

The data sheet for the phototransistor can be found here: https://www.arduino.cc/documents/datasheets/HW5P-1.pdf

Edit:
Thank you to everyone for the responses! I am just a little confused about how I could go about implementing some of the solutions. It appears to me as if the operational amplifier ones just increase the difference between the low and high states. Perhaps I was not detailed enough with my question. I have asked this question on the Arduino forum, which has a little more detail (my apologies for posting on two forums, but this is becoming urgent because of time constraints). The link to this forum is here: https://forum.arduino.cc/index.php?topic=452365.0.

Note: this question was initially written with the assumption that the device is a photoresistor. It was later updates to avoid confusion when searching for questions on photoresistors.