If you do not want Siri to bring up suggestions while using Spotlight search, you can find below the steps to Disable Siri Suggestions in Spotlight Search on iPhone.
Disable Siri Spotlight Search Suggestions on iPhone
The Spotlight Search feature on iPhone allows you to quickly search for Apps and other information by swiping down from middle of the screen and typing keywords in the Spotlight Search Bar.
As you can see in above image, Siri has already brought up its suggested Apps below the Search bar, based on the way this device has been used.
According to Apple, Siri Suggestions are designed to suggest actions that you are most likely to perform next, based on your daily routines and the way you use Apps on your iPhone.
If you do not find this useful, you can Turn OFF Siri Suggestions in Spotlight Search by going to Settings > Siri & Search and moving the toggle next to Show Suggestions & Show in Spotlight to OFF position.
After this, close the Settings screen > swipe down from middle of the screen and you will no longer find Siri Search Suggestions.
In general, users Disable Siri Suggestions in Spotlight Search to unclutter the Spotlight Search screen and to avoid being side-tracked or distracted by Siri Search Suggestions.