Ghoughpteighbteau? It's an example of a constructed word, used for illustration of irregularities in spelling in English. It is a respelling of the word 'potato', and like potato is pronounced /poʊˈteɪtoʊ/.
gh, pronounced /p/ as in hiccough /ˈhɪkəp/;
ough, pronounced /oʊ/ as in though /ðoʊ/;
pt, pronounced /t/ as in ptomaine /ˈtoʊmeɪn/;
eigh, pronounced /eɪ/ as in neigh /neɪ/;
bt, pronounced /t/ as in debt /dɛt/;
eau, pronounced /oʊ/ as in bureau /ˈbjʊəroʊ/.