from bs4 import BeautifulSoup

string ='''<a class="text-dotted show-phone__link js-show-phone">   5031  <span class="show-phone__visible">показать номер</span>
        <span class="show-phone__hidden">82403</span>
        </a>'''

soup = BeautifulSoup(string,'html.parser')
numb = soup.find('a',{'class':'text-dotted show-phone__link js-show-phone'}).text.split()[0:4:3]
print(numb)