Terrifying Packs have a guarantee that you’ll get Phobies from both of the scratch cards, when you first open it. However, after that there’s no guarantee and it’s all a matter of luck. I’m very unlucky and most of the time I don’t get even one Phobie. Do Horrific Packs also have a first-time guarantee? Because if they do, I’ll buy a Horrific Pack this time.
For Pack Odds & Information:
Terrifying Pack
Horrific Pack
Dreadful Pack
Clicking on the “i” icon when clicking on the pack will open those links and provide you with the information for the packs respectively. 
What does “Every 1.5 packs you can expect to receive a new Phobie” in the Terrifying Pack info page mean?
That may be a question best asked to our team over on our Discord. Unfortunately other than that page, I don’t have the insight that could answer that question for you. I do apologize for that. They should be able to provide a better answer there for you.
Ask the Devs - Discord Link