It is possible to request a taxi only.
The operating procedure is as follows.
1. Specify your desired Pickup location and Destination, then tap [Next].
2. Tap [Details].
3. Tap Taxi in the Details field, then tap [Set].
4. You will return to the "Step 2" screen. Tap [Request Taxi] to complete the process.
Ref.
Can I specify a rideshare car when making a car request?