Phrase searching in an inverted index

I am implementing a very rudimentary inverted index, and I am having trouble implementing a phrase searching method.

I have the following structure:

InvertedIndex.java: here I have a data structure:

private Map<String, ArrayList<Postings>> index = new HashMap<String, ArrayList<Postings>>(); 

where I store a word and a Posting list with all of the docId's and associated term positions in a document.

My Postings.java class has the following structure:

private Map<String, ArrayList<Integer>> postings; 

I have getters and setters for all of these data structures, so I am not including them because it would be too much for this post. The string is the docId, and the Arraylist holds all positions in a document for a word.

I have an class where I am implementing the following method to search by phrase:

    public ArrayList<String> searchByPhrase(String...terms){
        if (terms == null || terms.length < 2){
            return null; 
        }

        ArrayList<String> documents = new ArrayList<String>(); 

        for (int i = 0; i < terms.length; i++){
            ArrayList<Postings> postings1 = index.getPostings(terms[i]);
            if ((i + 1) < terms.length){
                ArrayList<Postings> postings2 = index.getPostings(terms[i+1]);

                int smaller = 0; 
                if (postings2.size() < postings1.size()){
                    smaller = postings2.size(); 
                }
                else {
                    smaller = postings1.size(); 
                }

                for (int j = 0; j < smaller; j++){
                        Postings p1 = postings1.get(j); 
                        Postings p2 = postings2.get(j); 
                        if (p1.containsID(p2.getDocId())){
                            System.out.println("FOUND MATCHING DOC");
                            //Do position checking in here
                        }   
                }
            }

        }


        return documents; 
    }

I know that within this method I have to check so that positions are within one spot away from each other. I have not yet implemented that because I want to first be able to find documents that are the same (which this is currently not doing). When I run this I get nothing back, and I have various documents that I know share words.

I want this method to be able to search for terms of various sizes ("hello world", "Thank you so much for your help", etc....). I feel like I am overcomplicating this, but I am very lost as to how to tackle it. Any suggestions would be appreciated.