JSFiddle - React, Tailwind, and code Playground

JavaScript

var array = [
  {
    id: 123, 
    name: 'Peter',
    phone: [null, null],
    addresses: [{ address1: 'Manchester, UK', address2: 'London, UK' }]
  },
  {
    id: 124,
    name: 'Sara',
    phone: [],
    addresses: [{ address1: 'London, UK', address2: 'Paris, FR' }]
  }
];

for(const entry of array) {
    const isEmpty = entry.phone.filter(p => p !== null).length === 0;
    entry.phone = isEmpty ? 'empty' : entry.phone;
}

console.log(array);