Ahh, I see the issue, it has a trailing new line.
Try this:
#!/bin/bash
phone_number="$1"
if [ -z "$phone_number" ]; then
echo "Usage: $0 <phone_number>"
exit 1
fi
# Increment the counter for the phone number
value=$(/usr/bin/redis-cli INCR "$phone_number")
# Set/refresh expiration to 300 seconds
/usr/bin/redis-cli EXPIRE "$phone_number" 300 >/dev/null
# Uncomment the following to log and troubleshoot
echo "$phone_number $value" >> /home/asterisk/CustomScripts/busylog.txt
# Check rate and print action
if [ "$value" -ge 5 ]; then
echo -n "block"
else
echo -n "continue"
fi