How do I report someone for abuse in Skype on mobile or tablet?

When you block a contact, you can also choose to report abuse. Reporting abuse notifies us of spammers so we can stop them in the early stages of their activity. 

Android (6.0+), Android tablet, iPhone, and iPad 

1. From Chats, find the contact you want to block, tap and hold their name, and then tap Block. 
2. Tap Report abuse from this person, select a reason, and then tap Block. 

Android mobile 4.0.4 - 5.1

1. From Chats, find the contact you want to block and tap their name.
2. Tap the menu   button, and then tap Block contact. 
3. Tap Report abuse from this person, select a reason, and then tap Block.